1.6.4 Fault detecting programme

Fault detecting programme for pumps

Mainly applicable to centrifugal pumps, but certain parts also apply to other types of pumps.

Fault detecting programme

Type of fault	Cause	Effect
1. Pump not working (no flow)	Pump not properly filled with liquid at start Excessive suction lift. Air admitted into suction pipe or through packings. Delivery head greater than pump was designed for. Incorrect loss calculation. Impeller blocked. Blockage in pipe network (closed valve). Fault in electric motor (eg. loss of phase).	Low power consumption. Rattling cavitation sound. No pressure. Pump releases liquid before delivery pipeline is filled. Too high pressure. New List Item Usually Iow power consump- tion and vibrations due to imbalance. High pressure if the fault is on the pressure side.
2. Capacity of pump reduced (too Iow flow or delivery head)	Wrong direction of rotation of electric motor. Too Iow speed (motor or transmission fault). Impeller back to front on shaft. Excessive suction lift (hot liquid pumps: too little supply head). Air admitted into suction pipe or through packings. Formation of gas in pumped liquid Increased losses in pipe sys- tem due to blockages or other forms of throttling. Impeller more or less blocked. Damage to impeller or excessively worn sealing rings.	Rate of flow and pressureonly about half normal values. Very high power consump- tion. Rattling cavitation sound. Pump operates noisily and releases liquid jerkily. Frequent rattling sounds from pump. Higher pressure and Iower rate of flow. Usually Iow power consump- tion. Vibrations or jarring sounds from pump.
3. Power requirement (cur- rent consumption) of pump excessive.	Delivery head Iower than estimated. Too high speed. Higher viscosity or density of pumped liquid than estima- ted. Packing glands too tightly adjusted. Mechanical damage to the pump such as damaged sealing rings. Incorrect alignment. Blockage of impeller	High rate of flow, usually Iow degree of efficiency. Rate of flow and possibly pressure greater than estima- ted. For density power multiplied with SG. High temperature of stuffing boxes. Jarring sounds, vibrations. Vibrations Can cause excessive power consumption, but usually the opposite.
4. Vibrations and jarring sounds in the pump	Poor alignment due to faulty installation, change of position, tension in pipes. Coupling faults such as imbalance, loose bolts or wear. Fault in electric motor. Damaged bearings. Impeller out of balance. Considerabie cavitation. Formation of gas or admix- ture of air in pumped liquid.	High bearing temperature Pressure oscillations Rattling sound in pump.
5. Leakage in rotating mechanical seals.	Damaged seal faces due to wear, contaminants in fluid, too high pressure or too high temperature. Cracked rings due to Shaft deflection, etc. Hang-up caused by block- ages or too hard O-rings.
6. Damage to stuffing boxes.	This kind of fault is a one. Below is a list of the most common types of damage to packing rings, causes and actions to be taken.	Sometimes gives rise to jarring sounds or overheating.
Internally burnt out External scratches Packing has extruded under box bottom or gland Packing has gone into adjacent ring Rings nearest to the gland severely compressed Packing in the box bottom has dissolved Packing in the box bottom full of impurities Packing has different dimensions on sides of shaft	Suggests wrong quality of packing or too tight adjustment. Replace packjng or change instruction. Shows that the packing has been rotating With the shaft. Packings under-dimensioned. Use a larger size. Shows that the play between box and Shaft or between gland and Shaft is too great. Insert a hard packing ring next to box or gland. Shows that the packing is cut too short. Check that the proper Iength is used. Shows that many packing rings were tightened simul- taneously. Using the appropriate tool, tighten every pack- ing individually. Shows that the packing is not resistant to the purngxi Iiquid. Change packing material. Shows that the sealant has not functioned as it should. Check pressure and quantity of barrier fluid. Indicates Shaft eccentricity. Realign.

Studying wear on shafts and sleeves is of assistance when tracing faults involving packings. Abnormal wear at the gland points to the wrong packing material or hard adjustment of the gland. This can be remedied by using a different quality packing material or by increasing the running leakage. Abnormal wear on the box bottom suggests the admission of impurities into the box. The remedy is to install or improve the barrier fluid. If it is necessary to tighten the box more often than usual, the reason is either that the shaft is out of alignment or that the packing material is unsuitable for the working conditions. Check shaft and or change to a more suitable quality of packing.